A man is suing the prison service after he developed post-traumatic stress disorder (PTSD) from rats running across his body and bed while he was locked in his cell, the Guardian has learned.

The 71-year-old was serving a short sentence at Wormwood Scrubs prison in west London after being convicted of a benefits offence which he insists he did not commit.

As a result of the rodents’ constant presence, he began to have vivid and terrifying nightmares, was diagnosed with depression and developed a skin rash and symptoms of PTSD.

The case has come to light the week after a damning report into HMP Bedford found that the rat problem there was so bad that one prisoner was witnessed catching and killing rats in his cell during the inspection.

The report, published on Tuesday, found that pest control work had failed to eradicate a significant infestation of the rodents at HMP Bedford.

When the pensioner at Wormwood Scrubs began to serve his time, one prison officer described the place as a “rathole” to him, while another told him the wing he had been assigned to was “worse than Beirut”.

The rat problem at the prison appears to be longstanding. A 2015 report into conditions at the jail by HM Inspectorate of Prisons referred to the issue thus: “The prison had a significant rat problem. We saw them every day and night we visited the prison and a large rats’ nest was very obvious in the grounds,” inspectors stated.

The man’s first encounter with the rats was the day after he arrived, when one came and sat on his feet while he was reading a newspaper in his cell. After that he saw rats many times: running up and down the walls, running across his bed, and getting in and out through the broken window of his cell.

“My cellmate used to eat smoky bacon crisps, and when he dropped a packet on the floor, the rats would get into the packets and finish off the crisps. They were so tame, they weren’t scared of humans at all,” he told the Guardian.

The problem was made worse by the fact that he was usually locked in his cell for 23 hours on weekdays and permanently over the weekends, meaning there was no escape from the rats.

He said rodents were also found in the servery area where prisoners got their food. “You should have heard the sound of so many grown men screaming when a rat jumped out of a sack of potatoes,” he said.

The man’s lawyer, Jane Ryan at Bhatt Murphy Solicitors, is bringing a claim against the Ministry of Justice on his behalf for a variety of issues, including a breach of his human rights and of the Equality Act, and for negligence.

She said that the appalling living conditions had had a devastating impact on the pensioner. “Living conditions in prisons should be humane for the benefit of staff and prisoners,” said Ryan.

Although the man has now been released from prison, he says that he is still haunted by fear of rats.

“There is not a day that goes by when I’m not looking at the walls to see if I can see rats running up and down them,” he said. “I’m getting a lot of anxiety attacks and I can’t sleep at night. I make sure I always keep my windows closed. Whenever I complained about the rats while I was in prison, the prison officers said to me: ‘This isn’t a hotel, you know. You’re here to be punished.’”